Underpowered 3901 Tractor with BH77 Backhoe (or design flaw)??

[ade678]

Hi All,

I recently purchased a brand new 3901 tractor with several hydraulic attachments — including a BH77 — and quickly noticed that the backhoe seemed sluggish and underpowered. The most obvious problem is that it won’t smoothly perform dual functions. For example, if I try to raise the boom first, the implement will then only very slowly curl the bucket. It's far inferior to the 2501 525/77BH or 26B TLB setup which I've rented a number of times.

The tractor is now back at the dealership (I called them about 30 minutes after they dropped it off, which was a bummer). They've run a handful of diagnostics on both tractor and backhoe, and they also seem surprised by the slow and uncoordinated performance. The best guess we’ve got comes from the Kubota factory itself: the machine is running too many implements on its hydraulic circuit.

Specifically, the tractor is equipped with (1) a front-loader, (2) a 3rd function valve, (3) a set of 3 rear aux hydraulics (for top & tilt), and (4) a BH77, connected in that order. Kubota’s guess is that the slow backhoe performance is due to the weak hydraulic flow by the time the fluid gets to the implement. A few numbers from tests done at the shop: At source, the pump is putting out 6.5 gal/min (as per factory spec). The flow rate drops to 5.7 gal/min after it crosses the front loader valve, then to 5.1 g/m after is crosses the 3rd function, and finally to 3.8 g/m by the time it crosses the rear auxiliaries and arrives at the backhoe.

Put simply: I'm asking a 3901 to do too much.

Still, I’m surprised that a 3901 can’t fully manage the load (or that that the company would sell it without a “3 implement max” warning.) Anyone experience something similar? If indeed it’s the hydraulics, then perhaps a diverter valve at the the rear aux directly to the BH77 would solve the problem? Or should I ask Kubota to switch to a model strong enough to power the implements I want? I get that a tractor isn’t rigged to function like a skidsteer or a mini ex, but a TLB configuration with a 3rd function and aux hydraulics seems like a reasonable setup.

Thoughts?

Thanks in advance to everyone on the forum for your time and opinions!

 

[ayak]

I have the same configuration but in a 3301 and it works flawlessly. There’s verbiage in the BH77 manual (p7 of the document/p17 of the pdf) that discusses how to prevent damage to the backhoe valve if these other options are also on the tractor.

 

[Nicfin36]

I know almost nothing about hydraulics, but I feel like they don't have something configured properly. I just don't buy that the L3901 cannot do it. I don't have rear hydraulics, but I have everything else you do and no problems with the L2501 and BH77. I have never read anything here like your problem and I am sure there are many L3901 owners with a backhoe and exact same features as yours.

 

[ade678]

I have the same configuration but in a 3301 and it works flawlessly. There’s verbiage in the BH77 manual (p7 of the document/p17 of the pdf) that discusses how to prevent damage to the backhoe valve if these other options are also on the tractor.

Thanks for the advice! Are you referring to the warning to keep the hydraulic control lever in the lowest position? I'm pretty sure that's where it been the entire time, but I'll check again. Any other items you suggest I check? Something else downstream of the BH valve? In any case, the fact that your 3301 works flawlessly confirms my guess that there's something wrong with my machine.

 

[ade678]

I know almost nothing about hydraulics, but I feel like they don't have something configured properly. I just don't buy that the L3901 cannot do it. I don't have rear hydraulics, but I have everything else you do and no problems with the L2501 and BH77. I have never read anything here like your problem and I am sure there are many L3901 owners with a backhoe and exact same features as yours.

Thanks for taking time to reply. I expect that you're right that something's not configured correctly. The dealership has been as accommodating and helpful as possible -- they've lent me a skidsteer and mini ex to use while they troubleshoot the issue -- so I wonder what they could be missing!

 

[ade678]

One other item: The first time the dealership examined the BH77 unit, they found a small bit of plastic in the hydraulic line (or perhaps relief valve?). Their guess is that it was a small bit of excess seal from factory production, and not too unusual. Still, I can't help but think something's just not right.

 

[kubotafreak]

A simple test for them to confirm that there is too much restricion through all those valves, is to place the backhoe after the loader valve. Then disconnect all the others. If there is no change than obviously there is something else wrong.

 

[Nicfin36]

If they have another backhoe on the lot, they could swap backhoes. If the problem goes away, it is something within the backhoe.

 

[MapleLeafFarmer]

I have the same configuration but in a 3301 and it works flawlessly. There’s verbiage in the BH77 manual (p7 of the document/p17 of the pdf) that discusses how to prevent damage to the backhoe valve if these other options are also on the tractor.

I too have a 3301 with BH77 and the BH has been flawless and smooth. The power it has seems to match the size/weight of the tractor well. If I want I can pick rear tires off the ground with boom/dipper, and really jerk the machine around if I wanted to be rough with it.
Wouldn't want it any stronger or could risk a rookie doing some damage to the machine. I believe its sized properly in my case.

 

[ade678]

If they have another backhoe on the lot, they could swap backhoes. If the problem goes away, it is something within the backhoe.

Thought of that. Unfortunately BH77s are rare in these days of supply chain issues. They do have a B26 on the lot for rent; I wonder if we could try running it off the the same lines.

 

[ade678]

I too have a 3301 with BH77 and the BH has been flawless and smooth. The power it has seems to match the size/weight of the tractor well. If I want I can pick rear tires off the ground with boom/dipper, and really jerk the machine around if I wanted to be rough with it.
Wouldn't want it any stronger or could risk a rookie doing some damage to the machine. I believe its sized properly in my case.

Any other implements attached?

 

[ayak]

Any other implements attached?

In my use of the BH77, I typically have on my FEL bucket (instead of the grapple), so that negates use/need of the 3rd function valve.
And anytime the BH77 is going on, I’m taking off my 3-pt hardware and cylinders (which means I’m not using my 3-rear remotes—no hydraulic thumb), so nothing there either. And I will zip-tie down the 3-pt Lift Lever to the lowest position.
With my backhoe dolly, I can switch back and forth in under 30 minutes (and that includes warming up the line tractor) when going between using my 3-pt/rear remotes and the BH77.

 

[TheOldHokie]

Hi All,

I recently purchased a brand new 3901 tractor with several hydraulic attachments — including a BH77 — and quickly noticed that the backhoe seemed sluggish and underpowered. The most obvious problem is that it won’t smoothly perform dual functions. For example, if I try to raise the boom first, the implement will then only very slowly curl the bucket. It's far inferior to the 2501 525/77BH or 26B TLB setup which I've rented a number of times.

The tractor is now back at the dealership (I called them about 30 minutes after they dropped it off, which was a bummer). They've run a handful of diagnostics on both tractor and backhoe, and they also seem surprised by the slow and uncoordinated performance. The best guess we’ve got comes from the Kubota factory itself: the machine is running too many implements on its hydraulic circuit.

Specifically, the tractor is equipped with (1) a front-loader, (2) a 3rd function valve, (3) a set of 3 rear aux hydraulics (for top & tilt), and (4) a BH77, connected in that order. Kubota’s guess is that the slow backhoe performance is due to the weak hydraulic flow by the time the fluid gets to the implement. A few numbers from tests done at the shop: At source, the pump is putting out 6.5 gal/min (as per factory spec). The flow rate drops to 5.7 gal/min after it crosses the front loader valve, then to 5.1 g/m after is crosses the 3rd function, and finally to 3.8 g/m by the time it crosses the rear auxiliaries and arrives at the backhoe.

Put simply: I'm asking a 3901 to do too much.

Still, I’m surprised that a 3901 can’t fully manage the load (or that that the company would sell it without a “3 implement max” warning.) Anyone experience something similar? If indeed it’s the hydraulics, then perhaps a diverter valve at the the rear aux directly to the BH77 would solve the problem? Or should I ask Kubota to switch to a model strong enough to power the implements I want? I get that a tractor isn’t rigged to function like a skidsteer or a mini ex, but a TLB configuration with a 3rd function and aux hydraulics seems like a reasonable setup.

Thoughts?

Thanks in advance to everyone on the forum for your time and opinions!

That's a very substantial drop in flow rate - more than I would expect for sure. The remotes are particularly bad for some reason - possibly the size of the inlet/outlet fittings?

The L3901 has the flow you need - the plumbing is the problem. This is a good example of why the back hoe should be higher up in the food chain.

Dan

 

[GreensvilleJay]

Sounds like there's more 'plastic' in the system somewhere. There shouldn't be any drop in GPM if it's an 'open center' system. Full 6.5 GPM should be available all the way to the furthest device, less friction losses( a wee amount).

 

[mikester]

Hi All,

I recently purchased a brand new 3901 tractor with several hydraulic attachments — including a BH77 — and quickly noticed that the backhoe seemed sluggish and underpowered. The most obvious problem is that it won’t smoothly perform dual functions. For example, if I try to raise the boom first, the implement will then only very slowly curl the bucket. It's far inferior to the 2501 525/77BH or 26B TLB setup which I've rented a number of times.

The tractor is now back at the dealership (I called them about 30 minutes after they dropped it off, which was a bummer). They've run a handful of diagnostics on both tractor and backhoe, and they also seem surprised by the slow and uncoordinated performance. The best guess we’ve got comes from the Kubota factory itself: the machine is running too many implements on its hydraulic circuit.

Specifically, the tractor is equipped with (1) a front-loader, (2) a 3rd function valve, (3) a set of 3 rear aux hydraulics (for top & tilt), and (4) a BH77, connected in that order. Kubota’s guess is that the slow backhoe performance is due to the weak hydraulic flow by the time the fluid gets to the implement. A few numbers from tests done at the shop: At source, the pump is putting out 6.5 gal/min (as per factory spec). The flow rate drops to 5.7 gal/min after it crosses the front loader valve, then to 5.1 g/m after is crosses the 3rd function, and finally to 3.8 g/m by the time it crosses the rear auxiliaries and arrives at the backhoe.

Put simply: I'm asking a 3901 to do too much.

Still, I’m surprised that a 3901 can’t fully manage the load (or that that the company would sell it without a “3 implement max” warning.) Anyone experience something similar? If indeed it’s the hydraulics, then perhaps a diverter valve at the the rear aux directly to the BH77 would solve the problem? Or should I ask Kubota to switch to a model strong enough to power the implements I want? I get that a tractor isn’t rigged to function like a skidsteer or a mini ex, but a TLB configuration with a 3rd function and aux hydraulics seems like a reasonable setup.

Thoughts?

Thanks in advance to everyone on the forum for your time and opinions!

Congrats on the new garage ornament. When reality sets in the truth hurts. The issue is unrealistic expectation, not a design flaw.

Now go buy/rent a real construction machine to do the jobs you want done. Save the tractor for what it was designed for - garden work.

 

[ayak]

Congrats on the new garage ornament. When reality sets in the truth hurts. The issue is unrealistic expectation, not a design flaw.

Now go buy/rent a real construction machine to do the jobs you want done. Save the tractor for what it was designed for - garden work.

Working in my rock garden with my lawn ornament.

 

[BAP]

My bet would be that either the 3rd function valve, rear remotes or backhoe feed is plumbed wrong. Either in the wrong sequence or wrong size fittings. Also, their is a possibility that the 3rd function is stuck passing fluid through it when it isn’t supposed to dumping pressure.

 

[PoTreeBoy]

That's a very substantial drop in flow rate - more than I would expect for sure. The remotes are particularly bad for some reason - possibly the size of the inlet/outlet fittings?

The L3901 has the flow you need - the plumbing is the problem. This is a good example of why the back hoe should be higher up in the food chain.

Dan

I suspect the BH has to be last in line to prevent back pressure damage. Kubota seems to like BH valves without 'T' lines.

 

[PoTreeBoy]

Sounds like there's more 'plastic' in the system somewhere. There shouldn't be any drop in GPM if it's an 'open center' system. Full 6.5 GPM should be available all the way to the furthest device, less friction losses( a wee amount).

I agree. That loss of flow makes no sense. This is a series system so 'flow in' equals 'flow out'. The only other place it has to go is to tank if there are tank connections, and then only if the valve is leaking.

 

[TheOldHokie]

My bet would be that either the 3rd function valve, rear remotes or backhoe feed is plumbed wrong. Either in the wrong sequence or wrong size fittings. Also, their is a possibility that the 3rd function is stuck passing fluid through it when it isn’t supposed to dumping pressure.

Quite possibly undersize fittings/hose, or a stuck spool. I dont think sequence matters. All things the dealer should be able to find and rectify pretty easily. It would be interesting to know what the pressure drop is across each valve and what that looks like with the remotes out of the circuit.

Dan